US 2009/0071118 A1 discloses a method and a system for modulating the modified Wobbe index (MWI) of a fuel which is supplied to a gas turbine, wherein a heat exchanger is used to preheat the fuel and the MWI of the incoming fuel is monitored, wherein the MWI considers the temperature of the fuel.
US 2010/0275609 A1 discloses a hybrid Wobbe control during rapid response start-up, wherein a temperature of a fuel to be ignited within a combustor of a gas turbine is determined and an additive is introduced into the combustor of the gas turbine when the temperature of the fuel is less than the target temperature.
U.S. Pat. No. 6,490,867 B2 discloses a method of operating a burner and burner configuration, wherein a calorific value of the fuel is determined and the degree of opening of a control element is calculated and directly set using the output and the calorific value resulting in a variable output control that is operationally reliable with respect to perturbations.
Thereby, the calorific value of the fuel is determined from the mass flow and the calorific value of the water and the mass flow and the calorific value of the heating oil.
U.S. Pat. No. 7,854,110 B2 discloses an integrated fuel gas characterization system for determining the amount of energy provided by the fuel prior to combustion of the fuel in the combustion stage, wherein the integrated fuel gas characterization system can include a Wobbe Meter for measuring the Wobbe index of fuel gas before the fuel gas is combusted in the gas turbine and wherein the control system may be designed to adjust one or more operating parameters of the gas turbine engine based on the rate of change of the Wobbe index.
U.S. Pat. No. 7,950,216 B2 discloses a gas turbine engine fuel control system, wherein a controller calculates a desired flow rate based at least on the combustive energy value of the fuel which has been determined by a combustive energy value evaluator, wherein the energy value evaluator determines an energy value of the fuel mixture either directly by measurement or by reference to tables based on mixture ratios.
Thereby, the LHV of the fuel can be determined using the measured temperatures and air mass flow rates of the engine.
U.S. Pat. No. 7,565,805 B2 discloses a method for operating a gas turbine engine system, wherein a processor is programmed to receive a signal indicative of a heating value of the fuel and automatically controls a fuel split between the fuel injection points on the combustor using the determined heating value, wherein fuel nozzles are designed to operate within a limited range of pressure ratios and changes in heating value and fuel gas temperature are accommodated for by increasing or decreasing the fuel nozzle gas passage area. The modified Wobbe index (MWI) represents a measure of the energy injected into the combustor for a given upstream and downstream pressure across a given fuel nozzle gas orifice and is calculated using the fuel lower heating value, the specific gravity with respect to air and the fuel temperature. Further, automatically modulating fuel gas splits in combustor using measured or calculated fuel gas MWI is disclosed.
EP 2 450 551 A2 discloses systems and methods for compensating fuel composition variations in a gas turbine, the method including monitoring at least one fuel parameter associated with a turbine combustor; monitoring one or more combustion dynamics characteristics associated with the turbine combustor; monitoring one or more performance and emissions characteristics associated with the turbine; estimating fuel composition based at least in part on the at least one fuel parameter, the one or more combustion dynamics characteristics, and the one or more performance and emissions characteristics, and adjusting at least one fuel parameter based at least in part on the estimated fuel composition.
Calorimeters may have been used for monitoring fuel properties where gas fuel composition varies, but the slow update rates may have made it difficult to produce effective control loops which maintain stable engine operation. Limiting the allowable rate of change of the fuel properties may help to remedy this problem but this may be often an unacceptable constraint for a particular operation condition or user application. Further, determination of the fuel property purely based on estimation using an engine model may lack accuracy.
It has been observed that conventional methods for controlling a supply of a fuel to a combustor of a gas turbine may not in all circumstances or operating conditions address the issue for maintaining a desired operation of the gas turbine or a stable operation of the gas turbine, when the kind, type or composition of the supplied fuel changes. Further, it has been observed that calorimeter measurements of fuel properties may be too slow in situations of rapidly varying gas composition. Further, conventional methods for estimating of properties of the fuel from engine parameters has been observed to be fast but may be prone to inaccuracies and drift problems.
Thus, there may be a need for a method and for an arrangement for controlling a supply of a fuel to a combustor of a gas turbine, wherein situations in which fuel changes can be handled, in order to provide a stable operation of the gas turbine.